Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Wednesday, June 13, 2012

Why doesn't Peters find Dinosauria or Saurischia?

Peters has defended his amniote analysis as being superior to other published analyses, since it includes numerous genus-level OTUs. And in this he is correct, though there are other measures of analysis quality too. One obvious example is the number of characters. There's no hard and fast rule regarding how many characters are needed to analyze a certain number of taxa, but you should at least include all characters previously utilized for the clade you're examining, unless some are invalid for whatever reason. Peters' analysis has a large number of areas in which it differs not only from the consensus, but from any other proposed phylogeny. One of these is his Dinosauria, which instead of the standard Ornithischia vs. Saurischia dichotomy, with the latter including Theropoda and Sauropodomorpha, has...

Thus it has an equivalent of Phytodinosauria and includes a host of non-dinosaurian taxa. Now, Saurischia is one of those clades (like Ornithothoraces) that while near-ubiquitous in published analyses, only takes a few extra steps to negate, so I'm not biased against it a priori. And I've said half-seriously before that ornithischian-like silesaurids and theropod-like shuvosaurines and hallopodines could threaten dinosaurian monophyly. Peters no doubt thinks his results are superior to the consensus, but did he actually test the consensus? Let's see which saurischian and dinosaurian synapomorphies (based on only the unambiguous synapomorphies of Nesbitt, 2011) Peters included in his analysis.

Saurischia

Yes- (1) Subnarial foramen between the premaxilla-maxilla where the border of the foramen is present on both the maxilla and the premaxilla (12-1)*.
(12) Metacarpal IV shaft width significantly narrower than that of metacarpals I–III (261-1).
(13) Distal end of pubis expanded relative to the shaft (5 pubis boot) (283-1).

No- (1) Exoccipitals do not meet along the midline on the floor of the endocranial cavity (115-1)*. Also in Crocodylomorpha and Effigia + Shuvosaurus.
(2) Supratemporal fossa present anterior to the supratemporal fenestra (144-1).
(3) Epipophyses present in postaxial anterior cervical vertebrae (186-0)*.
(4) Apex of deltopectoral crest situated at a point corresponding to more than 30% down the length of thehumerus (230-1)*.
(5) Radius shorter than 80% of humerus length (241-1).
(6) Proximal articular surfaces of the ischium with the ilium and the pubis separated by a large concave surface (297-2)*.
(8) Fourth trochanter asymmetrical, with distal margin forming a steeper angle to the shaft (317-1).(9) Cnemial crest arcs anterolaterally (328-2)*.
(10) Distinct proximodistally oriented ridge present on the posterior face of the distal end of the tibia (336-1)*.
(11) Proximal articular facet for fibula of the astragalus occupies less than 0.3 of the transverse width of the element (362-1).
(12) Concave articular surface for the fibula of the calcaneum (378-2).

Wow! Peters included 3 (17%) of saurischian characters and 1 (8%) of dinosaurian characters and didn't recover either clade? Who'd have thunk? In general, Peters' postcranial characters are few and usually reflect gross morphology. Wanna know the humeral characters included? Humerofemoral length and torsion. The tibial ones? Tibioilial length. Distal tarsal characters? None. Peters is fond of saying his sister taxa "look similar", and this is why- the characters reflect a general morphotype.

There's a reason making an amniote analysis is so challenging. It'd be easy enough to enter 300 taxa into Rieppel's or Mueller's analyses, but at that resolution, you need to add more characters to arrange taxa right within each subclade. Peters has not done this, but I'd bet doing so, and defining his states better, would result in a more standard topology, albeit one that may have genuine surprises.

3 comments:

I doubt much of the arguments and reconstructions of Peter. Too bad because you have time and talent, but it goes very wrong demonstrations.

By the way, and excuse the change of subject:

I just read the article Kurzanov, Efimov, and Gubin, 2003 and I think the course Allosaurus sp. Russia is actually a Ceratosauridae because he is associated more with Labrosaurus sulcatus and stechowi.

Well, Kurzanov et al. claim their material is similar to sulcatus and stechowi, but I don't see how it is. The Russian teeth don't have longitudinal grooves, which is why sulcatus and stechowi are usually referred to Ceratosauridae. Furthermore, the Russian teeth lack mesial serrations, unlike the lateral teeth of stechowi and Ceratosaurus (and Allosaurus). Ceratosaurus anterior teeth lack mesial serrations, but the figured Russian tooth is a lateral one based on its cross section. Once I redo my carnosaur page (which is long overdue), I'll probably move their entry to Coelurosauria (are there any ceratosaurs or carnosaurs that lack mesial serrations on lateral teeth?).